1. Field of the Invention:
This invention relates to an artificial joint and, more particularly, to an artificial joint for a finger or the like.
2. Description of the Prior Art:
There is known an artificial joint comprising a spherical articulatory member and a member having a complementarily concave surface in which the spherical member is fitted. There is also known an artificial joint comprising a pair of articulatory members each having a hole through which a pin extends to, join them. There is also known an artificial joint comprising members formed from a soft material, such as a resin or rubber. All of these joints have, however, their own drawbacks.
The artificial joint including a spherical member is required to have a very accurate shape in order to be capable of flexing smoothly. The manufacture of an accurately shaped joint is very difficult and requires a great deal of time and labor. This type of joint cannot be used for a finger or any other part of the body that is usually required to move only in two directions in a single plane, since one of its members is rotatable in all directions relative to the other.
The joint including a pin has the advantage that the pin restricts the articulatory members to rotation in only two directions. The pin, however, adds to the number of the parts forming the joint and increases the time required for assembling the joint for implantation. Moreover, the pin must have such a small diameter that a load bearing on it presents serious problems from the standpoint of durability and wear resistance.
The formation of sliding portions from a soft material also has a number of drawbacks. They are movable only to a limited extent and certain muscular force is required for maintaining them in their flexed positions. They are not satisfactory in fatigue strength.